While many road surfaces are constructed from hardened surfaces such as asphalt or concrete, tires are also frequently used in “off road” applications such as mud, gravel, sand, compacted soil, and other surfaces where the material of the surface can become loaded into the tread pattern. For example, mud can fill part or all of the grooves or other features of a tread pattern as the tire rotates during use. As the grooves or other features fill and the tire becomes loaded with mud, traction can be adversely affected as the effective tire surface becomes slick. In such case, the vehicle may become immobile or stuck. However, if the tire can self-clean or remove these materials during rotation, then the tread features have an opportunity to provide traction and thereby move the vehicle. In an ideal tire construction, during each rotation the non-contacting portions of the tread would release materials before rotating back into contact with the ground or road surface.
In addition to providing ornamental features attractive to the buyer, tread patterns may be developed for the purpose of improving traction in off road applications such as those mentioned above. In order to explore the self-cleaning efficacy of a proposed tread pattern, one or more tires can be constructed bearing the proposed pattern. In turn, these tires can then be placed on a test vehicle and subjected to various off road conditions in order to evaluate traction performance. Unfortunately, such an approach is expensive because e.g., a tire mold must be created or modified for each pattern change, the new tire must be manufactured, and then vehicle testing must be performed in off road conditions.
FIGS. 1-4 illustrate an alternative where testing can be performed with just a portion of the tire tread. More specifically, apparatus 100 of FIGS. 1-4 provides an exemplary embodiment of a device that may be used to test the self-cleaning ability of a tire tread pattern, which is also described in a copending application owned by applicants' assignee. Apparatus 100 allows for testing only a portion of the tread pattern without the necessity of manufacturing the actual tire replete with tread. For example, FIG. 4 depicts a tread sample 10, which provides a portion of a tread pattern for which evaluation of the pattern's ability to self clean is desired. Sample 10 may, for example, represent one pitch of a proposed tread pattern. Sample 10 may contain a completely new pattern or may include modifications of an existing pattern for which improvements in traction are being targeted. Larger or smaller portions of the overall tread pattern may also be used for testing with apparatus 100.
Sample 10 is loaded into a carriage 105 of apparatus 100. A plurality of pegs 110 on the non-tread side of sample 10 connect into multiple apertures 115 defined by carriage 105. Using fasteners 120, carriage 105 is attached to a mount 125 on apparatus 100. Sample 10 is loaded with materials 15. More particularly, as best shown in FIGS. 3 and 4, the grooves 20 in tread sample 10 are filled with materials 15 intended to be representative of the conditions a tire might encounter in off road operation. A variety of materials 15 may be used for testing. For example, materials such as clay, sand, and or silt may be combined with water to create a paste or “mud” that is loaded into the grooves 20 of tread sample 10.
Referring now to FIGS. 1 through 3, mount 125 is attached to an arm 130 carried upon a shaft 135 along with arms 140 and 145. Weights 150 and 155 are carried by arms 140 and 145 and counter the weight of tread sample 10, carriage 105, and mount 125 so that rotation as indicated by arrows R will be balanced about shaft 135. Shaft 135 is driven by motor 160, the speed of which can be controlled and/or measured. More specifically, the rate of acceleration, deceleration, and speed of motor 160 can be controlled and/or measured so as to create a known amount of centrifugal acceleration of tread sample 10 and materials 15 from a known rpm profile.
As sample 10 is rotated, centrifugal forces acting upon materials 15 will cause all or part of such materials to release from the tread. Images of the rotation of sample 10 and the subsequent release of materials 15 are captured by camera 170. Housed in box 185, camera 170 is connected to a camera eye 175 by wiring harness 180. Eye 175 is positioned at the end of support member 165 and rotates in synchronization with sample 10 to record the effect of the centrifugal forces on materials 15. Camera 170 may be selected from a variety of types and configurations to facilitate the recording of multiple visual images during the rotation of tread sample 10 and release of material 15. As used herein, “record” or “recording images” includes the use of a multiple different cameras and media types for visually capturing the response of materials 15 to the centrifugal forces that will be created during the rotation of sample 10. To ensure proper illumination of sample 10 and minimize the effects of other light sources during testing, apparatus 100 includes a light source 190 that also rotates in synchronization with sample 10 and camera 170. Apparatus 100 is one example of a device that may be used to provide recorded images of the release of materials 15 during the rotation of sample 10. Using the teachings disclosed herein, it will be understood that other devices could be used rotate a tire or a portion of its tread pattern and to record the release of materials such as mud from the tread.
While the recorded images provided from devices as apparatus 100 may be analyzed subjectively, the ready comparison of multiple different tread patterns using such images is difficult to accurately perform using only the raw, recorded images. More specifically, accurately determining the self-cleaning efficacy of various tread patterns and features using only the recorded images would be time consuming and subjective. A method of converting the images recorded by apparatus 100 into quantitative data for analysis and development is needed. More specifically, it would be very useful to have a method of converting the recorded images into numerical values that can be manipulated, graphically displayed, and otherwise studied for purposes of evaluating and developing tire self-cleaning ability. These and other advantages of the present invention will be apparent from the description that follows.